1. Field of the Invention
The present invention relates to a prismatic battery module and a method for manufacturing the same. More particularly, the invention relates to a prismatic battery module which is made by connecting a plurality of cells together and designed to reduce an internal resistance, and a method for manufacturing the same.
2. Description of Related Art
A conventional rechargeable battery module made by connecting a plurality of cells together, each having an individual cell case, has a problem that the connection path between the cells is long and the number of connection points in the battery module is large, thereby increasing the component resistance leading to the increase of internal resistance thereof.
In consideration of the aforementioned conventional problem, the inventors of this invention have proposed a prismatic battery module 100 including a plurality of cells 2 as shown in FIGS. 32 and 33. Reference numeral 3 denotes a prismatic battery case constructed in such a manner that a plurality of prismatic cell cases 4 of cells 2, each cell case having short lateral walls and long lateral walls, are integrally connected together in series, and each pair of cell cases shares short lateral walls thereof as a separation wall 5, and further, an upper opening of each of the cell cases is closed by a unitary lid 6. In the upper portions of outer short lateral walls of the outermost cell cases and the separation wall 5 between the adjacent cell cases 4 are formed connection holes 7. Within each of the cell cases 4, an electrode plate group 8 constructed by alternately stacking rectangular positive and negative electrode plates interposing a separator therebetween is accommodated together with an electrolyte. The positive and the negative electrode plates constituting the electrode plate group 8 project from the electrode plate group in opposite directions to form a lead portion 9a of the positive electrode plate and a lead portion 9b of the negative electrode plate, respectively. To the side ends of the lead portions 9a, 9b are connected collector plates 10a, 10b, respectively, by welding or the like.
In the upper portions of the collector plates 10a, 10b are formed connection projections 11 to be fitted into the connection holes 7, and the connection projections 11 of the collector plates 10a, 10b as positive and negative poles respectively are connected to each other between the adjacent cell cases 4 by welding. Furthermore, in the connection holes 7 of the outer short lateral walls of the outermost cell cases 4 are mounted connection terminals 12 as either a positive or negative pole, and a connection projection 13 of the connection terminal 12 and the connection projection 11 of either the collector plate 10a or 10b are connected to each other by welding. Thus, a plurality of cells 2 accommodated in the prismatic battery case 3 are connected together in series.
Additionally, in the lid 6 are provided a communication path 14 for balancing the internal pressure between the cell cases 4, a safety vent (not shown) for discharging the pressure when the internal pressure of the cell case 4 exceeds a predetermined value and a sensor fixing hole 15 for fixing a temperature sensor thereto to detect the temperature of the cell 2.
According to the above-described construction of battery, since the electrical communication path from the positive and negative electrode plates of the electrode plate group 8 to the respective lead portions 9a, 9b is short and further the adjacent lead portions 9a, 9b of the associated electrode plate groups are connected to each other via the associated collector plate 10a, 10b within the prismatic battery case 3, the connection path between the electrode plate groups is short and the number of connection points is small, thereby allowing the prismatic battery module to reduce the component resistance included therein and in proportion thereto, reduce the internal resistance.
However, although the prismatic battery module 100 shown in FIGS. 32 and 33 is constructed so that the connection path from the positive and negative electrode plates to the respective collector plates 10a, 10b via the respective lead portions 9a, 9b is short, as is denoted by arrows in FIG. 34, the adjacent collector plates 10a, 10b of the associated electrode plate groups are connected at one point of both ends of the connection projections 11 located at the upper portions of the adjacent collector plates by welding and therefore, there have been seen problems that the entire connection path between the adjacent electrode plate groups becomes longer and in addition, the internal resistance between the cells becomes higher since the electrical communication between the adjacent collector plates is performed at only one point. Furthermore, there have also been seen problems that the collector plates 10a, 10b employed in the battery 100 increases the manufacturing cost of battery correspondingly, and further, it is necessary to arrange the collector plates 10a, 10b on both sides of the electrode plate group 8 and to form the upper portion of the collector plates 10a, 10b so as to project beyond the upper end of the electrode plate group 8, thereby forcing enlargement of the volume of the cell case 4.